(display "ex1-8: ")

(define (good-enough? new old)
    (< (abs (/ (- new old) old)) 0.00001))

(define (improve guess x)
    (/ (+ (/ x (* guess guess)) (* 2 guess)) 3))

(define (cbrt-iter guess x)
    (if (good-enough? guess (improve guess x))
        guess
        (cbrt-iter (improve guess x) x)))

(define (cbrt x)
    (cbrt-iter 1.0 x))

(display (cbrt 100))